1. Technical Field
This disclosure relates to a treatment-liquid application device and an image forming apparatus, and more specifically to a treatment-liquid application device that applies treatment liquid to treatment-liquid application targets, such as image recording media, and an image forming apparatus including the treatment-liquid application device.
2. Description of the Related Art
Image forming apparatuses are known as, for example, printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities, and different types of image forming methods for the image forming apparatuses are also known. As one type of image forming apparatus, for example, image forming apparatuses employing a liquid-ejection recording method are known that use at least one recording head to eject droplets of ink. During image formation, such liquid-ejection-type image forming apparatuses eject droplets of ink or other liquid from the recording head onto an image recording medium to form (record or print) a desired image to the image recording medium.
The term “image recording medium” used herein is not limited to a sheet of paper but includes an OHP (overhead projector) sheet or anything on which liquid, e.g., ink droplets, or solid, e.g., toner particles, constituting images can be adhered. In other words, the term “image recording medium” is used as a generic term including a recording medium, a recorded medium, a recording sheet, and a recording sheet of paper.
Such liquid-ejection-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets from the recording head while moving the recording head in a main scanning direction of the carriage, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head held stationary in the image forming apparatus.
Such a liquid-ejection-type image forming apparatus may have image failures, such as “feathering” in which dots formed with liquid droplets blur in a jaggy shape on the image recording medium and “color bleeding” in which different types of liquid droplets (e.g., ink droplets of different colors) mix each other at adjacent areas on the image recording medium to blur color boundaries. Such a liquid-ejection-type image forming apparatus may also take a relatively long time to dry liquid droplets on the image recording medium after image formation.
To minimize such failures, conventionally, a prescribed treatment liquid may be applied to the image recording medium before image formation to minimize migration of liquid droplets landed on the image recording medium or reduce the drying time of liquid droplets landed on the image recording medium.
For example, JP2008-260307-A, JP2007-301814-A, and JP2010-194526-A propose that a treatment liquid for reacting to ink to minimize image or color bleeding is applied to an image recording medium with an application roller before image formation. In a treatment-liquid application device described in JP2008-260307-A, a scooping roller serving as a treatment-liquid carrier rotates and the roller surface of the scooping roller moves in and out a treatment liquid in a direction perpendicular to the roller shaft while entering and soaking in the treatment liquid stored in a treatment liquid tank of a liquid chamber, thus scooping the treatment liquid. When the roller surface of the scooping roller indirectly contacts the roller surface of an application roller serving as a treatment-liquid applicator via a film-thickness control roller, the treatment liquid on the roller surface of the scooping roller is applied to the roller surface of the application roller. When a transport roller serving as a transport unit transports the image recording medium serving as a treatment-liquid application target so as to pass a nipping portion between the application roller and the transport roller, the treatment liquid on the roller surface of the application roller is adjusted to a certain thickness and applied to the image recording medium. Surplus treatment liquid on the application roller is transferred onto the scooping roller indirectly contacting the application roller, and the scooping roller passes the treatment liquid stored in the liquid chamber to return the surplus treatment liquid to the treatment liquid stored in the liquid chamber.
Alternatively, in JP2007-301814-A and JP2010-194526-A, after transfer of the treatment liquid onto the image recording medium, a blade-shaped cleaning member contacts the roller surface of the application roller to collect surplus treatment liquid remaining on the roller surface of the application roller after the transfer.
However, in JP2008-260307-A, foreign matter adhered to the image recording medium, e.g., paper dust adhered to a sheet of paper is transferred onto the roller surface of the application roller at the nipping portion between the application roller and the transport roller, and further transferred onto the scooping roller indirectly contacting the application roller. When the scooping roller enters and passes the treatment liquid in the liquid chamber, a vortex is generated in the liquid chamber by friction of the roller surface of the scooping roller with the treatment liquid. Although the foreign matter can be separated and removed from the roller surface of the scooping roller by the shearing force of the vortex, foreign matter remains in the treatment liquid of the treatment liquid tank. The foreign matter in the treatment liquid is agitated by the vortex in the treatment liquid tank without settling at the bottom of the liquid chamber, thus increasing contamination of the treatment liquid in the liquid chamber.
Alternatively, in JP2007-301814-A and JP2010-194526-A, by contacting a blade-shaped cleaning member with the roller surface of the application roller adhered with foreign matter such as paper dust, the treatment liquid including the foreign matter can be collected and removed from the roller surface. However, friction dust occurs due to the friction of the blade-shaped cleaning member with the roller surface of the application roller, and adheres to the roller surface of the application roller. When the cleaning member contacts the adhered friction dust, the friction dust separates and detaches from the roller surface of the application roller, floats in the air, and adheres to the image recording medium. As a result, if an image is formed on the image recording medium having the adhered friction dust, the friction dust may separate from the image recording medium, thus causing missing of requisite image elements. Alternatively, the friction dust permeated with ink may migrate over the image recording medium, thus degrading the image surface. Additionally, such friction dust may mix into the treatment liquid stored in the liquid chamber and increasingly contaminate the treatment liquid, resulting in a reduced treatment performance of the treatment liquid.